The human cataract is one of the leading causes of world blindness. During this past year, 300,000-400,000 cataract extractions were done in the United States alone. Vision Research, A National Plan, indicates the priority of understanding lens pathophysiology such that a medical treatment or cure would be possible. We have recently concluded the first in vivo animal study of cataractagenesis using laser light scattering. Abnormalities detected appeared to be the earliest in vivo changes noted. The sensitivity and quantitative aspects of this technique offer advantages over those methods presently available. It is known that diabetic patients display an early and accelerated onset of cataractagenesis and vitreous hemorrhage as compared to non-diabetics. Approximately 50% of those patients undergoing vitrectomy exhibit lens opacities during this procedure. This group of patients is also at a higher risk for the long-term development of cataracts so that some surgeons routinely remove the lens at the time of surgery. Lens removal during vitrectomy increases the hazards of the procedure, the incidence of rubeosis iridis and the final visual acuity is not as satisfactory. Laser light scattering measurements will be performed on patients undergoing vitrectomy surgery. This population appears well suited for this experiment because it provides a short-term model for cataractous development in an already high risk population that is unavailable in humans elsewhere in a predictable fashion. It will provide us with an opportunity that should, in short-term fashion, prove the applicability of our system to human lens research, as well as define that population of patients that will develop cataracts. With this information, we hope to predict preoperatively which lenses will result in cataracts postoperatively. In addition to allowing an intelligent decision to be made regarding cataract surgery in the vitrectomy candidate, the technique will have broad applicability to basic and clinical research aimed at preventing cataract formation. We believe that techniques such as laser light scattering, capable of the reproducible pre-clinical detection of cataract and quantification, are necessary before clinical trials of cataract prevention, such as aldose reductase inhibitors, are possible.